The process of manufacturing a semiconductor integrated circuit (IC) device may be very complicated and expensive. Therefore, prior to actually manufacturing the IC device, the IC device may be subjected to a simulation process verifying that it is operated according to a specified design. The most representative program used for an operation simulation of a circuit is a simulation program with integrated circuit emphasis (SPICE). The SPICE simulates a circuit model by using equations mathematically defining the operation of several circuit devices included in the circuit design and then provides the results as verification information. In order to simulate the circuit, various devices should be modeled. For this, a Berkeley short-channel (BSIM) insulated-gate field effect transistor (IGFET) has been the most widely used.
A varactor may be implemented having a MOS structure in a semiconductor integrated circuit device. Such a MOS varactor may have a high Q index and may occupy a small area when compared to a pn junction-type varactor. The MOS varactor may be used as an LC tank of a voltage controlled oscillator (VCO) for generating different VCO oscillating frequencies. The MOS varactor is one of important RF passive devices such as an analog filter, a switch capacitor circuit, a data converter, an RF circuit, and the like that may be applied to various fields. Since the characteristics of the MOS varactor may be varied according to the operating frequency, a physical geometry of the device, and a bias condition, an RF modeling is important.
However, in the modeling of the varactor, since the real component of impedance may be determined by the serial connection of R, L, and C, it may have a value that is not varied according to frequency. However, the real component in the actual measured value of impedance may vary according to frequency. The existing modeling method cannot explain this change. Accordingly, since it may be difficult to accurately model the device, the operation prediction of the circuit may not be accurate.
Moreover, optimally modeling the varactor using a CAD tool may be time-consuming and incurs a great deal of expense.